1. Field of the Invention
The present invention relates in general to anti-theft devices and more particularly pertains to anti-theft circuits for application to engine propelled vehicles having electrical ignition systems.
2. Description of the Prior Art
In the field of vehicle anti-theft devices it has been the general practice to employ apparatus of an electromechanical nature to disable the engine or to produce an audible alarm or a combination thereof. Inherent difficulties are present in the majority of these devices. For example, they are complex, large structures, difficult to install and repair, require maintenance and are so arranged that should they malfunction, the vehicle becomes disabled.
The present theory in designing anti-theft devices is to permit unauthorized use of the vehicle for a limited time. Such limited use by a thief will allow him to drive the vehicle for a short distance, which vehicle, then becomes disabled. The thief is now in unfamiliar or hostile surroundings and rather than expose himself to scrutiny while attempting to disarm the device, he will abandon his efforts and look elsewhere.
Timing networks such as those shown in U.S. Pat. Nos. 4,107,962, 4,004,273 or thermal time delay units as in U.S. Pat. Nos. 2,205,104 and 3,614,458 are used to initiate the disablement of an engine or vehicle at some predetermined time after it has been started. The precise disable function may be through a fuel pump, the ignition, battery or any other part vital to the engine's operation.
The majority of anti-theft devices presently on the market are large, complex and when in use dissipate considerable energy in the form of heat. Such structural characteristics do not permit the necessary freedom of location within the vehicle whereby they can be readily hidden from view, much less undetectable to an experienced thief. In addition, should the thief be aware of the existence of an anti-theft device, he may readily defeat the device or in attempting to do so, damage the device or the vehicle.
Another inherent disadvantage to present devices is the fact that the device must be armed or activated by the operator upon leaving the vehicle. Unless the operator is alerted or in some way reminded, he will on numerous occasions fail to arm the device, especially in view of the fact that the device is in a hidden location.
Accordingly, it is an object of this invention to provide a relatively simple, compact, inexpensive and reliable vehicle anti-theft device which is easily installed, readily hidden from view and requires minimum maintenance.
Another object is to provide an anti-theft device which after a predetermined time subsequent to starting the vehicle engine, will disable the ignition circuit and thereby prevent engine function.
A further object of this invention is the provision of an anti-theft device which is automatic in operation and which does not require arming by the operator but which device may be by-passed by the legitimate operator to permit use of the vehicle by others. Under the latter condition, the device will provide a signal to alert the operator that the device is in the disabled state when he again assumes control of the vehicle.
A still further object of this invention is to provide an anti-theft device which, while functioning, will not deplete the vehicle's electrical energy nor dissipate considerable amounts of heat when the ignition circuit is disabled.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing.